Vol. 27 No. 3 2025 3 EDITORIAL COUNCIL EDITORIAL BOARD EDITOR-IN-CHIEF: Anatoliy A. Bataev, D.Sc. (Engineering), Professor, Rector, Novosibirsk State Technical University, Novosibirsk, Russian Federation DEPUTIES EDITOR-IN-CHIEF: Vladimir V. Ivancivsky, D.Sc. (Engineering), Associate Professor, Department of Industrial Machinery Design, Novosibirsk State Technical University, Novosibirsk, Russian Federation Vadim Y. Skeeba, Ph.D. (Engineering), Associate Professor, Department of Industrial Machinery Design, Novosibirsk State Technical University, Novosibirsk, Russian Federation Editor of the English translation: Elena A. Lozhkina, Ph.D. (Engineering), Department of Material Science in Mechanical Engineering, Novosibirsk State Technical University, Novosibirsk, Russian Federation The journal is issued since 1999 Publication frequency – 4 numbers a year Data on the journal are published in «Ulrich's Periodical Directory» Journal “Obrabotka Metallov” (“Metal Working and Material Science”) has been Indexed in Clarivate Analytics Services. Novosibirsk State Technical University, Prospekt K. Marksa, 20, Novosibirsk, 630073, Russia Tel.: +7 (383) 346-17-75 http://journals.nstu.ru/obrabotka_metallov E-mail: metal_working@mail.ru; metal_working@corp.nstu.ru Journal “Obrabotka Metallov – Metal Working and Material Science” is indexed in the world's largest abstracting bibliographic and scientometric databases Web of Science and Scopus. Journal “Obrabotka Metallov” (“Metal Working & Material Science”) has entered into an electronic licensing relationship with EBSCO Publishing, the world's leading aggregator of full text journals, magazines and eBooks. The full text of JOURNAL can be found in the EBSCOhost™ databases.
OBRABOTKAMETALLOV Vol. 27 No. 3 2025 4 EDITORIAL COUNCIL EDITORIAL COUNCIL CHAIRMAN: Nikolai V. Pustovoy, D.Sc. (Engineering), Professor, President, Novosibirsk State Technical University, Novosibirsk, Russian Federation MEMBERS: The Federative Republic of Brazil: Alberto Moreira Jorge Junior, Dr.-Ing., Full Professor; Federal University of São Carlos, São Carlos The Federal Republic of Germany: Moniko Greif, Dr.-Ing., Professor, Hochschule RheinMain University of Applied Sciences, Russelsheim Florian Nürnberger, Dr.-Ing., Chief Engineer and Head of the Department “Technology of Materials”, Leibniz Universität Hannover, Garbsen; Thomas Hassel, Dr.-Ing., Head of Underwater Technology Center Hanover, Leibniz Universität Hannover, Garbsen The Spain: Andrey L. Chuvilin, Ph.D. (Physics and Mathematics), Ikerbasque Research Professor, Head of Electron Microscopy Laboratory “CIC nanoGUNE”, San Sebastian The Republic of Belarus: Fyodor I. Panteleenko, D.Sc. (Engineering), Professor, First Vice-Rector, Corresponding Member of National Academy of Sciences of Belarus, Belarusian National Technical University, Minsk The Russian Federation: Vladimir G. Atapin, D.Sc. (Engineering), Professor, Novosibirsk State Technical University, Novosibirsk; Victor P. Balkov, Deputy general director, Research and Development Tooling Institute “VNIIINSTRUMENT”, Moscow; Vladimir A. Bataev, D.Sc. (Engineering), Professor, Novosibirsk State Technical University, Novosibirsk; Vladimir G. Burov, D.Sc. (Engineering), Professor, Novosibirsk State Technical University, Novosibirsk; Aleksandr N. Korotkov, D.Sc. (Engineering), Professor, Kuzbass State Technical University, Kemerovo; Dmitry V. Lobanov, D.Sc. (Engineering), Associate Professor, I.N. Ulianov Chuvash State University, Cheboksary; Aleksey V. Makarov, D.Sc. (Engineering), Corresponding Member of RAS, Head of division, Head of laboratory (Laboratory of Mechanical Properties) M.N. Miheev Institute of Metal Physics, Russian Academy of Sciences (Ural Branch), Yekaterinburg; Aleksandr G. Ovcharenko, D.Sc. (Engineering), Professor, Biysk Technological Institute, Biysk; Yuriy N. Saraev, D.Sc. (Engineering), Professor, V.P. Larionov Institute of the Physical-Technical Problems of the North of the Siberian Branch of the RAS, Yakutsk; Alexander S. Yanyushkin, D.Sc. (Engineering), Professor, I.N. Ulianov Chuvash State University, Cheboksary
Vol. 27 No. 3 2025 5 CONTENTS OBRABOTKAMETALLOV TECHNOLOGY Kondratiev V.V., Gozbenko V.E., Kononenko R.V., Konstantinova M.V., Guseva E.A. Determination of the main parameters of resistance spot welding of Al-5 Mg aluminum alloy..................................................................................... 6 Gvindjiliya V.E., Fominov E.V., Marchenko A.A., Lavrenova T.V., Debeeva S.A. Infl uence of cutting speed on pulse changes in the temperature of the front cutter surface during turning of heat-resistant steel 0.17 C-Cr-Ni-0.6 Mo-V................................................................................................................................................................ 23 Karelin R.D., Komarov V.S., Cherkasov V.V., OsokinA.A., Sergienko K.V., Yusupov V.S., Andreev V.A. Production of rods and sheets from TiNiHf alloy with high-temperature shape memory eff ect by longitudinal rolling and rotary forging methods.................................................................................................................................................................... 37 EQUIPMENT. INSTRUMENTS Zakovorotny V.L., Gvindjiliya V.E., Kislov K.V. Information properties of vibroacoustic emission in diagnostic systems for cutting tool wear................................................................................................................................................ 50 Zhukov A.S., Ardashev D.V., Batuev V.V., Kulygin V.L., Schuleshko E.I. Modal analysis of various grinding wheel types for the evaluation of their integral elastic parameters...................................................................................... 71 Nishandar S.V., Pise A.T., Bagade P.M. Numerical and experimental investigation of heat transfer augmentation in roughened pipes................................................................................................................................................................ 87 Nosenko V.A., Rivas Perez D.E., Alexandrov A.A., Sarazov A.V. The eff ect of the grinding method on the grain shape coeffi cient of black silicon carbide....................................................................................................................................... 108 MATERIAL SCIENCE Karlina Yu.I., Konyukhov V.Yu., Oparina T.A. Investigation of the process of surface decarburization of steel 20 after cementation and heat treatment.................................................................................................................................. 122 Kovalevskaya Z.G., Liu Y. Eff ect of heat treatment on the structure and properties of high-entropy alloy AlCoCrFeNiNb0.25............................................................................................................................................................. 137 Sirota V.V., Prokhorenkov D.S., Churikov A.S., Podgorny D.S., Alfi mova N.I., Konnov A.V. Corrosion properties of coatings produced from self-fl uxing powders by the detonation spraying method............................................................ 151 Filippov A.V., Shamarin N.N., Tarasov S.Yu., Semenchyuk N.A. The infl uence of structural state on the mechanical and tribological properties of Cu-Al-Si-Mn bronze............................................................................................................. 166 Waheed F., Qayoom A., Shirazi M.F. Fabrication, characterization and performance evaluation of zinc oxide doped nanographite material as a humidity sensor......................................................................................................................... 183 Dolgova S.V., Malikov A.G., Golyshev A.A., Nikulina A.A. Features of the structure of gradient layers «steel - Inconel - steel», obtained by laser direct metal deposition.................................................................................................. 205 Burkov A.A., Dvornik M.A., Kulik M.A., Bytsura A.Yu. The infl uence of tungsten carbide particle size on the characteristics of metalloceramic WC/Fe-Ni-Al coatings.................................................................................................... 221 Patil S., Chinchanikar S. Investigation on the mechanical properties of stir-cast Al7075-T6-based nanocomposites with microstructural and fractographic surface analysis...................................................................................................... 236 EDITORIALMATERIALS 252 FOUNDERS MATERIALS 263 CONTENTS
OBRABOTKAMETALLOV Vol. 23 No. 3 2021 MATERIAL SCIENCE EQUIPMENT. INSTRUMENTS 7 5 Numerical and experimental investigation of heat transfer augmentation in roughened pipes Siddhanath Nishandar 1, a, Ashok Pise 1, b, Pramodkumar Bagade 2, c, * 1 Department of Mechanical Engineering, Government College of Engineering, Karad, Shivaji University, Kolhapur, Maharashtra 445414, India 2 Department of Mechanical Engineering, TSSM’s Bhivarabai Sawant College of Engineering and Research (BSCOER), Narhe, Pune, Maharashtra 445414, India a https://orcid.org/0000-0001-6190-3412, siddhant.nishandar04@gmail.com; b https://orcid.org/0009-0003-0276-8996, ashokpise@gmail.com; c https://orcid.org/0000-0002-4069-1542, pramodbagade@gmail.com Obrabotka metallov - Metal Working and Material Science Journal homepage: http://journals.nstu.ru/obrabotka_metallov Obrabotka metallov (tekhnologiya, oborudovanie, instrumenty) = Metal Working and Material Science. 2025 vol. 27 no. 3 pp. 87–107 ISSN: 1994-6309 (print) / 2541-819X (online) DOI: 10.17212/1994-6309-2025-27.3-87-107 ART I CLE I NFO Article history: Received: 23 June 2025 Revised: 04 July 2025 Accepted: 10 July 2025 Available online: 15 September 2025 Keywords: Heat transfer enhancement Surface roughness Turbulent kinetic energy (TKE) Pulsating flow Turbulent flow Nusselt number (Nu) ABSTRACT Introduction. In many technical applications, such as thermal energy systems, chemical processing, power production, and HVAC, efficient heat transfer (HT) is essential. Research on improving HT performance in circular pipes is still crucial, especially when it comes to changes that cause thermal boundary layers to be disrupted and turbulence to grow. Purpose of the work: The purpose of this work is to thoroughly examine how convective heat transfer can be improved in circular pipes with purposefully roughened surfaces. It focuses on how surface roughness, flow pulsations, Reynolds number (Re), and heat flow rate (Q) affect thermal performance. Methods of investigation. A combination of experimental and numerical methods is employed to assess the thermo-fluid dynamics inside the pipe. Lab-scale experiments and computational fluid dynamics (CFD) simulations are used to investigate temperature distribution, velocity and pressure fields, turbulent kinetic energy (TKE), vorticity, eddy viscosity, local heat transfer coefficient (h), and Nusselt number (Nu). Additionally, sinusoidal pulsations are introduced at the inlet and the outlet, with regular oscillations in frequency (f) and amplitude (A), over a turbulent flow range (6,753 ≤ Re ≤ 31,000). Results and discussion. The results show that surface roughness enhances HT by significantly increasing turbulence and disrupting the thermal boundary layer. TKE becomes a significant factor when there is a strong correlation between higher HT coefficients and rising turbulence intensity. HT performance is further improved by introducing flow pulsations; downstream pulsation increases Nu by 20–22% and upstream pulsing by 16–19%. The outcomes demonstrate how effectively controlled flow pulsations and surface roughness combine to optimize heat transfer. This collaborative approach holds great potential for compact and highly efficient thermal system designs in industrial environments. For citation: Nishandar S.V., Pise A.T., Bagade P.M. Numerical and experimental investigation of heat transfer augmentation in roughened pipes. Obrabotka metallov (tekhnologiya, oborudovanie, instrumenty) = Metal Working and Material Science, 2025, vol. 27, no. 3, pp. 87–107. DOI: 10.17212/1994-6309-2025-27.3-87-107. (In Russian). ______ * Corresponding author Bagade Pramodkumar M., Ph.D. (Aerospace Engineering), Professor Department of Mechanical Engineering, TSSM’s Bhivarabai Sawant College of Engineering and Research (BSCOER), Narhe, Pune, 445414, Maharashtra, India Tel.: +91 9075279575, e-mail: pramodbagade@gmail.co Introduction To improve heat exchanger performance while lowering size and operating costs, several tactics have been investigated. These tactics are typically divided into two categories: passive and active. Passive methods – such as the use of finned or spirally roughened tubes – decrease the thickness of the thermal boundary layer and improve heat transfer (HT) by creating turbulence close to the tube wall. In recent years, these methods have drawn more attention. Active approaches, on the other hand, make use of external energy sources and include strategies like fluid pulsation, jet impingement, mechanical vibration, and the use of electrostatic fields to boost HT efficiency.
OBRABOTKAMETALLOV MATERIAL SCIENCE Том 23 № 3 2021 EQUIPMEN . INSTRUM TS Vol. 7 No. 3 2025 Concentrated temperature gradients can disrupt the boundary layer in both laminar and turbulent regimes, lowering thermal resistance and raising the local heat transfer coefficient, particularly in the presence of forced convection. Pulsating flow, in particular, is essential for modifying shear forces, boundary layer characteristics, and overall thermal resistance to improve HT. Consequently, there is currently significant interest in studying how pulsating flow affects convective heat transfer. Natural pulsating flows are found in many engineering systems, including: – eddy turbulence ‑ chaotic disturbances inherent in turbulent flow, leading to fluctuations in velocity and pressure. – turbomachinery ‑ periodic variations in pressure and velocity at the compressor and turbine blades, caused by rotor rotation and flow interaction with the blades. – transient flows ‑ changes caused by fluctuations in the system’s operational parameters. Practical applications of pulsating flows also include: – reciprocating internal combustion engines ‑ intake and exhaust systems characterized by periodic flow variations due to the engine’s operating cycles. – gas turbine engines ‑ flow oscillations caused by surge conditions. – positive displacement pumps: the operating principle of these pumps is based on generating pulsating flow. – human respiration ‑ airflow that spontaneously pulsates as part of human breathing. Although pulsating flows are sometimes perceived as undesirable disturbances, they can also enhance processes such as fuel-air mixing in combustion systems. The findings presented in the literature vary: some research indicates that heat transfer (HT) has improved, while others indicate that it has not improved at all or has even decreased. Important factors affecting heat transfer include surface geometry, pulsation location, Reynolds number (Re), Prandtl number (Pr), pulsation frequency (f), and amplitude (A). Description of the problem The heat transfer (HT) mechanisms in pulsating flow over roughened surfaces have not yet been fully clarified by previous studies, which are often limited to narrow parameter ranges. More research is required to determine how the placement of the pulsation source, surface roughness patterns, Reynolds number (Re), and pulsation frequency affect turbulent flow and heat transfer characteristics. Objectives The present study is conducted with the following objectives: 1. Investigate the effects of various factors affecting pulsating flow experimentally and numerically. 2. Establish empirical correlations based on the observed flow dynamics. 3. Analyze the effects of pulsation orientation on heat transfer. 4. Examine the differences between the performance of pulsating flow and steady-state flow. The scope and importance of the study Convective heat transfer is crucial for many engineering systems. Even though oscillatory flow has shown promise in enhancing heat transfer (HT), there is currently a scarcity of research on its application in thermal systems, specifically within pipe walls. Understanding the thermo-hydrodynamics of pulsating flow is crucial because higher HT leads to higher efficiency. This work fills that gap by focusing on circular pipes under sinusoidal pulsation. Future research will examine other pipe geometries and pulsation types that were not covered in this study. Pulsating flow heat transfer (HT) is essential to many industrial sectors, including thermoelectric and nuclear power [5, 6], food processing [7], pharmaceuticals [8], smart buildings [9], HVAC [10], transportation [11], agriculture [12], petrochemicals [13], material handling [14], bulk manufacturing [15], and many more. Increased HT efficiency has led to improvements in heat exchanger design, such as the use of innovative channel forms and compact tubing. Without sacrificing functionality, these developments raise volumetric power density and use less material. Rowin et al. investigated HT prediction
OBRABOTKAMETALLOV Vol. 23 No. 3 2021 MATERIAL SCIENCE EQUIPMENT. INSTRUMENTS 7 5 on uneven surfaces [16]. Qu et al. [17] demonstrated that internal capillary tube roughness significantly improves startup and operational stability in micro-pulsating heat pipes (PHPs). Surface tension, fluid viscosity, and wall roughness all affect flow resistance, which limits stable pulse operation in fixeddiameter PHPs [18]. Singh et al. [19] investigated ordered roughness and pulsed flow in microchannels using 2D simulations. Due to enhanced vortex activity, pulsation raised the Nusselt number (Nu) by up to 32.76% regardless of roughness. They also found that the optimal pulsation frequency varies with hydraulic diameter and that rough walls result in larger pressure decreases, even with heat transfer (HT) improvements. Wu and Cheng [20] discovered Nu fluctuations in shape-variable trapezoidal silicon microchannels. In waterfilled minichannels, Lin et al. [21] discovered that roughness heights between 18 and 96 μm improved HT. Lu et al. [22] confirmed that roughness raised flow resistance and Nu in laminar microchannel flows. Croce et al. [23] showed that roughness shape has a greater effect on pressure drop than Nu. Despite extensive research on pulsating flow dynamics, heat transfer (HT) mechanisms remain incompletely understood [24–32]. Analytical and numerical investigations in laminar flow [33–37] demonstrate localized HT effects, with pulsation-induced Nu fluctuations being dominant near the pipe entrance and decreasing downstream. Despite extensive research on pulsating flow dynamics, the underlying heat transfer (HT) mechanisms remain incompletely understood [24–32]. Analytical and numerical investigations in laminar flow regimes [33–37] demonstrate localized HT effects, wherein pulsation-induced Nu fluctuations are most pronounced near the pipe entrance and diminish in the downstream direction. Methodology Fig. 1 shows the experimental setup. A copper pipe, 400 mm in length and 28 mm in diameter, serves as the test section. Flexible joints hold it in place at both ends. Four K-type thermocouples are embedded in axial grooves on the outer surface of the pipe and connected to a multichannel recorder via a multipoint switch to record temperature measurements. A 400 mm long nickel-chromium heater (resistivity = = 15.5 Ω/m) provides uniform heat input. Airflow is provided by a 1.5 HP centrifugal blower (800 CFM), selected for its ability to maintain turbulent flow conditions. An electrically operated solenoid valve introduces flow pulsations. Operational boundaries are influenced by static pressure, temperature rise, and Reynolds number (Re). A flow control valve (¾” brass valve, 12V DC, 1.5 A/18 W, orifice size 25 mm, normally closed, stainless steel components), as shown in Fig. 2, is used to regulate airflow with a sub-second response time. The valve allows for adjustment of the pulsation mechanism to provide the required amplitude and frequency of pulsation. Fig. 1. Experimental set up Fig. 2. Flow control valve
OBRABOTKAMETALLOV MATERIAL SCIENCE Том 23 № 3 2021 EQUIPMEN . INSTRUM TS Vol. 7 No. 3 2025 Numerical Simulation Approach ANSYS Fluent was used for the simulations. The governing equations were the 3D Navier-Stokes equations (Eqs. 1–6), which incorporate eddy viscosity (μt), strain rate (Eij), and velocity components (ui). Energy transport was governed by Eq. (7). The friction factor and theoretical Nusselt number (Nu) were determined using Eq. (8) and the Dittus-Boelter correlation (Eq. 9) [38–41]. 0 ( ) ( ) ( ) p u v w t x y z ∂ ∂ ρ ∂ ρ ∂ ρ + + + = ∂ ∂ ∂ ∂ (1) 2 2 2 2 2 2 1 u u u p u u u u v w x y z x x y z ∂ ∂ ∂ ∂ ∂ ∂ ∂ + + = − + µ + + ∂ ∂ ∂ ρ ∂ ∂ ∂ ∂ (2) 2 2 2 2 2 2 1 v v v p v v v u v w x y z y x y z ∂ ∂ ∂ ∂ ∂ ∂ ∂ + + = − + µ + + ∂ ∂ ∂ ρ ∂ ∂ ∂ ∂ (3) 2 2 2 2 2 2 1 w w w p w w w u v w x y z z x y z ∂ ∂ ∂ ∂ ∂ ∂ ∂ + + = − + µ + + ∂ ∂ ∂ ρ ∂ ∂ ∂ ∂ (4) 2 ( ) ( ) i t t ij ij i j k j ku p k k E E t x x x ∂ ρ µ ∂ ρ ∂ ∂ + = + µ − ρε ∂ ∂ ∂ σ ∂ (5) 2 1 2 2 ( ) ( ) i t s t ij ij s i j s j u p k C E E C t x x x k k ∂ ρε µ ∂ ρ ε ∂ ∂ε ε ε + = + µ − ρ ∂ ∂ ∂ σ ∂ (6) v p T T T T k k k q C x x y y z z t ∂ ∂ ∂ ∂ ∂ ∂ ∂ + + + = ρ ∂ ∂ ∂ ∂ ∂ ∂ ∂ (7) 2 2 4 2 ; ( / ) / P m f V L D V D ∆ = = ρ ρπ (8) Nu = 0.023Re0.8Pr0.4 (9) Mesh Generation Mesh quality significantly impacts accuracy. A near-orthogonal grid with y⁺ = 0.5 (spacing y = 1.3628×10−5) ensures accurate wall resolution [42]. The structured mesh consisted of 1,283,136 nodes. Fig. 3 shows a cross-sectional view of the mesh. Velocity inlet conditions included a constant uniform profile for validation and a sinusoidal pulsing profile for dynamic cases, as defined by V = U₀[1 + A sin(2πft)], where A denotes amplitude, f frequency, t time, and U₀ mean velocity. A heat flux was applied at the wall, and a pressure outlet condition was established at the pipe exit. Boundary Conditions The following boundary conditions were applied: 1. A pulsating velocity profile was imposed at the inlet using a userFig. 3. Meshing at the cross section defined function for sinusoidal velocity input.
OBRABOTKAMETALLOV Vol. 23 No. 3 2021 MATERIAL SCIENCE EQUIPMENT. INSTRUMENTS 7 5 2. A constant heat flux boundary condition was applied to the pipe wall. 3. A pressure outlet boundary condition was applied at the pipe exit. The k-ε turbulence model was used to resolve turbulence effects. Validation The present study was validated against the results of Elshafie et al. [43], who investigated pulsating turbulent flow (10,000 ≤ Re ≤ 40,000; 6.6–68 Hz) in heated pipes. Numerical accuracy was confirmed by Fig. 4, which demonstrates excellent agreement in the average Nusselt number (Nu) between the present simulations and those of Elshafie et al. Fig. 5 depicts the transient variations in the surface heat transfer coefficient (h). The fluctuations stabilize after t = 2.5 s; therefore, t = 6 s was deemed sufficient for steady-state calculations. In all cases, h increases with Re. Fig. 4. Comparison of the average Nusselt number with the theoretical and experimental results of Elshafie [43] Fig. 5. Surface HT coefficient (h) obtained for different Re Effects of Surface Roughness Surface roughness enhances heat transfer (HT) by disrupting the thermal boundary layer [44], although it also increases pressure drop [45, 46]. Due to the complexity of the phenomena, extensive experimental research is required [47]. MacDonald et al. [48] demonstrated the impact of roughness on drag using direct numerical simulation (DNS) across sinusoidal surfaces (k⁺ = 10, λ = 0.05–0.54). Meyer et al. [49] reported that roughness increases HT in laminar flow but has a negligible influence in turbulent regimes. Abdelfattah et al. [56] investigated 48-element impinging jets with hemispherical, droplet, and cylindrical roughness elements; cylinders enhanced HT, while droplets reduced drag. Wall roughness affects momentum and energy transport [57]. Investigations of roughened pipes indicate that the log-law behavior is altered by a roughness function fr, based on the roughness height Ks+. Equation (10) is used to account for roughness in the velocity profile, where k = 0.4187 (von Karman constant). ANSYS Fluent classifies hydrodynamically smooth, transitional, and completely rough regimes based on the Cebeci-Bradshaw method, using ΔB and Ks+. 1 * * ln / p p w u u u y E B k ρ = − ∆ τ ρ µ (10)
OBRABOTKAMETALLOV MATERIAL SCIENCE Том 23 № 3 2021 EQUIPMEN . INSTRUM TS Vol. 7 No. 3 2025 Results and Discussion Elshafie et al. [43] experimentally studied pulsating turbulent airflow in a heated pipe under constant heat flux, a configuration relevant to modern industrial heat transfer applications. They examined pulsation frequencies ranging from 6.6 to 68 Hz and Reynolds numbers (Re) from 10,000 to 40,000. Their findings demonstrated that the Nusselt number (Nu) was significantly influenced by both Re and frequency (f), particularly in the entrance region, where changes were more pronounced than in the fully developed zone. The downstream position of the oscillator near the pipe exit affected the distribution of local heat transfer (HT). In this study, analogous investigations were conducted for Re = 13,350 to 37,100. Centerline velocity and total pressure increased with increasing Re, while the wall surface temperature decreased. These results are summarized in Table 1, which demonstrates that turbulent kinetic energy (TKE) and vorticity consistently increase with Re. Fig. 6 shows velocity profiles for Re = 37,100 under upstream pulsation, downstream pulsation, and no pulsation (A = 0.2, f = 6.7). The pulsing cases exhibit only slight variations in vorticity and lower velocities compared to the baseline (no pulsation) case. These patterns indicate that while pressure, velocity, TKE, and ω increase with increasing Re, surface temperature decreases. Consequently, h and Nu increase with Re, supporting the validity of the numerical method and exhibiting good agreement with theoretical and experimental findings from Elshafie et al. [43]. Ta b l e 1 Flow properties for various Re values Re Vmean (m/s) Vmax (m/s) Tmax (K) Press. (Pa) TKE ω (s −1) 10,850 7.1313 10.3 329 115 1.15 1.000 13,350 8.7745 12.5 325 160 1.6 1.250 16,800 11.0420 15.6 322 255 2.7 1.600 22,500 14.7885 20.8 320 465 5 2.100 24,650 16.2016 22.6 318 552 6 2.300 31,560 20.7433 28.8 316 925 10 2.800 37,100 24.3846 33 314.2 1.300 15 3.200 a b Fig. 6. Comparison of velocity (V) profiles along the pipe length for Re = 37,100, under steady-state (without pulsations) and pulsating flow conditions (A = 0.2, f = 6.7): a – DN pulsation = downstream pulsation; b – UP pulsation = upstream pulsation
OBRABOTKAMETALLOV Vol. 23 No. 3 2021 MATERIAL SCIENCE EQUIPMENT. INSTRUMENTS 7 5 Effect of location of pulsation This section reports the effects of pulsation location. Two cases were considered: – pulsation located downstream of the flow. – pulsation located upstream of the flow. Pulsation located at the downstream of the flow Fig. 7 illustrates the increase in the mean heat transfer (HT) coefficient with increasing Re and heat input (Q). The enhancement ranges from 20% to 27% at f = 3.33 Hz and Q = 100 W, and from 30% to 36% at f = 1 Hz. Tables 2 and 3 present values of h and Nu for various Re and Q without pulsation. As Re and Q increase, Nu increases steadily, indicating improved HT performance. Fig. 7. Heat transfer as a function of Re at varying heat input, with pulsation frequencies of f = 1 Hz and f = 3.33 Hz at downstream pulsation Ta b l e 2 Surface HT coefficient (h) at different Re and heat input without pulsation Experimental heat transfer coefficient, h Re Q = 25 W Q = 50 W Q = 75 W Q = 100 W 6,753 22.1 33.04 40.25 47.13 9,504 27.92 34.48 42.77 48.74 11,618 32.11 36.88 45.4 51.26 13,414 35.53 41.19 49.89 54.29 Ta b l e 3 Variations in Nu with Re at different heat input without any pulsation Nusselt number, Nu Re Q = 25 W Q = 50 W Q = 75 W Q = 100 W 6,753 23.43 31 37 44 9,504 29.59 32 40 45 11,618 34.04 34 42 48 13,414 37.66 38 46 50
OBRABOTKAMETALLOV MATERIAL SCIENCE Том 23 № 3 2021 EQUIPMEN . INSTRUM TS Vol. 7 No. 3 2025 Ta b l e 4 Nu at different heat inputs with pulsation frequency, f = 1Hz and 3.33Hz when pulsating mechanism is mounted downstream Reynolds number Nusselt number, Nu f = 1.0 Hz f = 3.33 Hz Re 25 W 50 W 75 W 100 W 25 W 50 W 75 W 100 W 6,753 31 34 40 46 44 47 55 58 9,504 33 35 43 49 48 52 62 67 11,618 36 38 47 51 54 54 62 67 13,414 42 45 51 55 56 60 67 71 Ta b l e 5 HT Coefficient vs. Reynolds Number at Various Heat Inputs for Pulsation Frequencies f=1Hz and 3.33 Hz when pulsating mechanism is mounted upstream Reynolds number Nusselt number, Nu f = 1.0 Hz f = 1.0 Hz Re 25 W 50 W 75 W 100 W 25 W 50 W 75 W 100 W 6,753 26 32 38 44 37 42 48 54 9,504 29 34 40 47 41 43 53 56 11,618 29 35 43 49 44 48 56 60 13,414 34 39 48 52 52 53 61 63 Nu demonstrably improves with increasing heat input. The findings indicate that as Re and heat input increase, the mean heat transfer coefficient (hmean) also increases. At f = 1 Hz, a 17–23% increase in the heat transfer (HT) coefficient is observed at Q = 100 W. Pulsation located at the upstream of the flow Similarly, upstream pulsation enhances heat transfer (HT) as Re and Q increase. At Q = 100 W and f = 1 Hz, the HT enhancement ranges from 22% to 26%, while at f = 3.33 Hz, it ranges from 29% to 33%. The generally higher Nu values observed under downstream pulsation, as shown in Tables 4 and 5, suggest its superior HT effect. Effects of pulsation frequency Table 6 shows that increasing the pulsation frequency (f) from 1 Hz to 3.33 Hz significantly increases the experimental heat transfer coefficient (hexpt.) and the experimental Nusselt number (Nuexpt.). For instance, at Re = 6753 during downstream pulsation, hexpt. rises from 32.91 to 47.15, and Nuexpt. rises from 30.96 to 44.36. Similarly, at Re = 13,414 and f = 3.33 Hz, hexpt. and Nuexpt. reach 60.75 and 57.15, respectively. Figs. 8, a–d illustrate the relationship between the Reynolds number (Re), heat input (Q = 25 W and 100 W), pulsation frequency (1 Hz, 3.33 Hz), pulsation location (upstream, downstream), the surface heat transfer coefficient (h), and the Nusselt number (Nu). Higher Re improves heat transfer at both heat inputs. In all cases, the 3.33 Hz pulsation produces the highest h and Nu values, particularly with downstream pulsation. Downstream pulsation consistently outperforms upstream pulsation. Both frequency and Re enhance thermal performance, with more pronounced effects at higher heat inputs (100 W). These trends indicate that pulsation settings are crucial for optimizing heat transfer.
OBRABOTKAMETALLOV Vol. 23 No. 3 2021 MATERIAL SCIENCE EQUIPMENT. INSTRUMENTS 7 5 Ta b l e 6 Experimental HT Coefficient and Nu for Different Res and Frequencies for Q = 25 W. DS= downstream; US=upstream Reynolds number hexpt. Nuexpt. f = 1.0 Hz f = 3.33 Hz f = 1.0 Hz f = 3.33 Hz Re DS US DS US DS US DS US 6753 32.91 28.21 47.15 39.99 30.96 26.54 44.36 37.62 9504 35.9 30.97 51.79 43.88 33.77 29.13 48.72 41.28 11618 38.53 31.59 58.5 47.15 36.25 29.72 55.03 44.36 13414 45.13 36.31 60.75 56.41 42.46 34.16 57.15 53.07 a b c d Fig. 8. Changes in Nu and h values as a function of Re for various pulsation frequencies at heat inputs of Q = 25 W and Q = 100 W Numerical Results Although the heat transfer (HT) coefficients and Nusselt number (Nu) values are derived from experiments, simulations provide a better understanding of the influencing flow mechanics. Fig. 9 displays vorticity contours under upstream pulsation for Re = 6753, Q = 954 W/m², A = 0.1, and f = 1 Hz. Shear-
OBRABOTKAMETALLOV MATERIAL SCIENCE Том 23 № 3 2021 EQUIPMEN . INSTRUM TS Vol. 7 No. 3 2025 induced turbulence is evidenced by vorticity peaks near the walls. Flow disturbances are evident near the core, and their impact diminishes beyond L = −0.25 m. Fig. 10 compares the velocity contours under upstream and downstream pulsation. In the upstream case, a longer high-velocity region extends toward the pipe exit, indicating a more widespread pressure drop and increased turbulence. Conversely, downstream pulsation localizes the high-velocity region, which may lead to concentrated pressure zones and non-uniform HT. Fig. 11 displays the pressure contours at t = 6 s. The peak pressure is higher downstream (63.21) compared to upstream due to the downstream pulsation, suggesting localized acceleration effects. Fig. 12 displays the turbulent kinetic energy (TKE) contours for upstream pulsation from t = 1 s to 6 s. TKE increases from 0.55 to 0.92 over time, indicating growing turbulence that enhances HT. The persistent and significant symmetry of the distribution promotes uniform HT. Although turbulent kinetic energy (TKE) development initiates and concentrates more rapidly near the boundaries, TKE increases overall, which aligns with the observed higher local heat transfer (HT). The symmetry and rapid increase in turbulence observed with downstream pulsation confirm its effectiveness in enhancing convective HT. Fig. 9. Velocity contour plots for Re = 6,753, heat input Q = 954 W/m², pulsation amplitude A = 0.1, pulsation frequency f = 1 Hz at downstream pulsation
OBRABOTKAMETALLOV Vol. 23 No. 3 2021 MATERIAL SCIENCE EQUIPMENT. INSTRUMENTS 7 5 Fig. 10. Comparison of velocity contours for Re = 6,753, heat input Q = 954 W/m², pulsation amplitude A = 0.1, pulsation frequency f = 1 Hz at downstream pulsation (left) and upstream pulsation (right) a b a b Fig. 11. Pressure contour plots in mid y-plane for Re = 6,753, heat input Q = 954 W/m², pulsation amplitude A = 0.1, pulsation frequency f = 1 Hz at downstream pulsation (left) and upstream pulsation (right)
OBRABOTKAMETALLOV MATERIAL SCIENCE Том 23 № 3 2021 EQUIPMEN . INSTRUM TS Vol. 7 No. 3 2025 These results demonstrate that pulsation, particularly when applied downstream, significantly enhances HT through increased turbulence, vorticity, and velocity variations. The primary mechanisms contributing to improved heat transport in pulsating flows are enhanced eddy formation and the generation of shear layers. Conclusion The enhancement of heat transfer (HT) in a circular pipe with surface roughness under turbulent flow conditions was investigated using a combined experimental and computational approach. The study focused on the effects of surface roughness, pulsation frequency (f), Reynolds number (Re), heat input (Q), and amplitude (A) on HT characteristics. Key parameters evaluated included velocity, pressure, and temperature distributions, turbulent kinetic energy (TKE), vorticity, eddy viscosity, the surface HT coefficient (h), and the Nusselt number (Nu). The following key conclusions can be drawn from the results: 1. TKE as a driver of HT enhancement: a) TKE is critical for the production and sustenance of turbulence, which dominates the pulsating heat transfer mechanism. b) Increased TKE strengthens fluid-wall interactions, enhancing convective HT, particularly with downstream pulsation as observed in this study. c) These results align with those of previous studies [2, 3, 4], even those that did not consider roughness effects [60]. Fig. 12. Turbulent kinetic energy (TKE) contour plots in the mid y-plane for Re = 6,753, heat input Q = 954 W/m², pulsation amplitude A = 0.1, pulsation frequency f = 1 Hz at upstream pulsation
OBRABOTKAMETALLOV Vol. 23 No. 3 2021 MATERIAL SCIENCE EQUIPMENT. INSTRUMENTS 7 5 2. Impact of pulsating flow: a) Pulsation, whether applied upstream or downstream, significantly affects turbulence parameters, with the downstream configuration exhibiting a more pronounced effect. b) For 6753 ≤ Re ≤ 31000, downstream pulsation enhanced HT by 20%–22%, while upstream pulsation improved HT by 16%–19%. c) Pulse intensity, governed by f and A, influences the extent of turbulence penetration. No single f and A combination consistently optimizes HT enhancement. Future work will focus on optimization studies to determine optimal parameter combinations. 3. Future directions: a) Future studies should investigate other fluids with varying viscosities and Prandtl numbers, such as water and oil. b) Analyses should be extended to non-circular pipe geometries, such as finned or rectangular channels. c) HT for non-Newtonian fluids under pulsating flow should be analyzed for applications in the food and pharmaceutical industries. d) Future work should combine advanced CFD with experimental validation to achieve reliable predictive modeling and optimization. In conclusion, this study demonstrates that the synergistic combination of surface roughness and pulsating flow effectively enhances HT performance, providing a promising approach for improving industrial heat exchanger applications. References 1. Ye Q., Zhang Y., Wei J. A comprehensive review of pulsating flow on heat transfer enhancement. Applied Thermal Engineering, 2021, vol. 196, p. 117275. DOI: 10.1016/j.applthermaleng.2021.117275. 2. YangB., GaoT., Gong J., Li J. Numerical investigationonflowandheat transfer of pulsatingflowinvarious ribbed channels. Applied Thermal Engineering, 2018, vol. 145, pp. 576–589. DOI: 10.1016/j.applthermaleng.2018.09.041. 3. Duan D., Cheng Y., Ge M., Bi W., Ge P., Yang X. Experimental and numerical study on heat transfer enhancement by flow-induced vibration in pulsating flow. Applied Thermal Engineering, 2022, vol. 207, p. 118171. DOI: 10.1016/j.applthermaleng.2022.118171. 4. Shang F., Fan S., Yang Q., Liu J. An experimental investigation on heat transfer performance of pulsating heat pipe. Journal of Mechanical Science and Technology, 2020, vol. 34, pp. 425–433. DOI: 10.1007/s12206-019-1241-x. 5. Ganapathy V. Steam generators and waste heat boilers: For process and plant engineers. Boca Raton, CRC Press, 2014. 539 p. ISBN 9781138077683. 6. Zohuri B. Application of compact heat exchangers for combined cycle driven efficiency in next generation nuclear power plants: A novel approach. Cham, Springer Nature Link, 2015. 366 p. eISBN 978-3-319-23537-0. DOI: 10.1007/978-3-319-23537-0. 7. Bassols J., Kuckelkorn B., Langreck J., Schneider R., Veelken H. Trigeneration in the food industry. Applied Thermal Engineering, 2002, vol. 22 (6), pp. 595–602. DOI: 10.1016/S1359-4311(01)00111-9. 8. Šalić A., Tušek A., Zelić B. Application of microreactors in medicine and biomedicine. Journal of Applied Biomedicine, 2012, vol. 10 (3), pp. 137–153. DOI: 10.2478/v10136-012-0011-1. 9. Sharma A., Tyagi V.V., Chen C.R., Buddhi D. Review on thermal energy storage with phase change materials and applications. Renewable and Sustainable Energy Reviews, 2009, vol. 13 (2), pp. 318–345. DOI: 10.1016/j. rser.2007.10.005. 10. Ameen A. Refrigeration and air conditioning. PHI Learning Pvt. Ltd., 2006. 512 p. ISBN 8120326717. ISBN 978-8120326712. 11. Oliet C., Oliva A., Castro J., Pérez-Segarra C.D. Parametric studies on automotive radiators. Applied Thermal Engineering, 2007, vol. 27 (11), pp. 2033–2043. DOI: 10.1016/j.applthermaleng.2006.12.006. 12. Heldman D., Moraru C.E., eds. Encyclopedia of agricultural, food, and biological engineering. 2nd ed. Boca Raton, CRC Press, 2010. DOI: 10.1201/9780429257599. 13. Coker A.K. Introduction. Coker A.K. Petroleum refining design and application handbook. John Wiley & Sons, 2018, ch. 1, pp. 1–6. ISBN 978-1-119-25710-3. DOI: 10.1002/9781119257110.ch1. 14. Coker A.K. Thermodynamic properties of petroleum and petroleum fractions. Coker A.K. Petroleum refining design and application handbook. John Wiley & Sons, 2018, ch. 4, pp. 63–110. DOI: 10.1002/9781119257110.ch4.
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